1906] BRIEFER ARTICLES 59 
cavities and hairs do not develop in the familiar way except where Nostoc 
colonies are, the liverwort must profit by such associates. It is simply a 
matter of mechanics. Where the resistance is less than growth can over- 
come (and this is the case between the Nostoc filaments in the gelatinous 
mass), the liverwort cells will grow out, forming short hairs. The growing 
and swelling colony as a whole will enlarge the cavity in which it lies. 
There are other intercellular spaces throughout the thallus, but these are 
not enlarged because not occupied. There is no conceivable advantage 
in their enlargement.—GEorcE J. Petrce, Stanford University, Cali- 
jornia. 
DISTRIBUTION AND HABITS OF SOME COMMON OAKS. 
SINCE writing the paper under this title, which appeared in the June 
number of this journal, I have been in Milwaukee and had the opportunity 
of examining the oaks in two herbaria, probably representative of any that 
may be found there. In the Public Museum were two specimens labeled 
Quercus palustris Du Roi. One had an acorn, and as far as determinable 
-by this and the leaf-characters, was Q. ellipsoidalis; it is certainly not what 
it is labeled. The other was without fruit, and was doubtless the same 
species. In the herbarium of Dr. Lewis SHERMAN, one of the older 
residents of Milwaukee and an acquaintance of Dr. LAPHAM, was a speci- 
men labeled as above. It had an acorn cup but no nuts. This showed 
at least that it was not Q. palustris. All the evidence tends to the con- 
clusion that the real pin oak does not occur in the region from which 
these specimens were taken.—E. J. Hut, Chicago. 
